A multiplicity of air-powered paint spraying systems exist in the prior art which as a rule comprise an apparatus for air flow generation, for example, a compressor or a fan, and a spray gun. If a relatively small paint supply is used, it is fastened to the spray gun (see, for example, EP 1 602 411 B1). If a relatively large paint supply is provided, it is handled in a separate and stationary manner, for example, in a bucket or container, the operating part with paint spraying lance and spray head representing a transportable part and being connected via a connector hose (see, for example, WO 2011/038712 A1).
In what are known as HVLP (high-volume, low-pressure) systems, the paint is atomized in a known way at a low air and paint pressure by means of a large air volume, for example, by a fan. This differs, for example, from what is known as an airless method, in which the paint is atomized by way of very high paint pressure. Here, the fan and the paint pump are either accommodated in the gun unit or, as an alternative, in a base unit. The air and the paint are combined in the spray head and the paint is atomized in a known way.
In the case of a multiple-piece paint spraying system with a separate base station, the paint transport takes place via a paint pump which is provided in the base station, sucks in the paint from a paint bucket or another storage container and delivers it to the paint spray gun or a paint roller or the like via a paint hose which is possibly several meters long. Depending on the viscosity of the paint and the length of the paint hose and the relatively small cross section of the paint hose, a considerable paint pressure is necessary on the part of the paint pump in the base station, in order to deliver the paint to the paint application tool, for example, a paint roller, brush or a paint spray gun. In the case of highly viscous paints and a paint hose length of, for example, more than from 5 m to 8 m and a paint hose internal diameter of, for example, only from 6 mm to 8 mm, paint pressures of from 2 bar to 8 bar are necessary, for example, in order to overcome the pressure drop which occurs in the paint hose. Here, the actual spraying operation in the paint spray gun is carried out at a relatively low paint pressure of, for example, only from approximately 0.3 bar to 0.4 bar.
The pressure reducing device/pressure regulator which is essential as a constituent part in the present invention is described and claimed in detail in the parallel patent application having the file number DE 10 2014 104 982.9. Reference is made hereby to the disclosure of the patent application and its contents are made the contents of this application by way of reference.
As a result of the long hose and the associated elasticity effects, for example, as a result of a partially elastic hose material or the inherent dynamic inertia of the transported liquid (paint), a considerable hysteresis is produced between the pressure which is provided by the paint pump at the base station and the pressure at the transportable element, for example, the paint roller or the paint spray gun.
In particular, the spraying operation at the spray head itself should be carried out at an appropriately lower pressure, in order to avoid uncontrolled paint discharge, what is known as “spitting” during opening of a needle valve on the spray head. If this is not realized, an inhomogeneous paint application results on account of fluctuating dispensed quantities of atomizable paint at the paint spray head. In the prior art, this effect is avoided by way of switching the paint delivery on and off in accordance with the paint quantity to be dispensed. However, this necessitates complex and brief switching operations which make the corresponding units complicated, susceptible to disruption and expensive. Paint rollers or paint brushes also have to be supplied continuously with paint, without material pulses of paint being dispensed when a valve is opened.
In the context of the invention, a paint inlet line is to be understood to mean a line of the type which is provided for feeding paint to a paint dispensing apparatus, for example, to a spray gun, and is connected upstream of a pressure regulator. In the context of the invention, a paint inlet line can also be understood to mean a paint hose.
In the context of the invention, a paint dispensing line is to be understood to mean a line of the type which is connected downstream of a pressure regulator and is provided for feeding paint to the outlet of a paint dispensing apparatus, for example a spray gun. In the context of the invention, the paint dispensing line is arranged within a paint dispensing apparatus, for example a spray gun.